1. Field of the Invention
This invention relates to a combination system of an illuminating device and an image pick-up device and to improvements in the illuminating device and the image pick-up device.
2. Description of the Prior Art
Generally, an image pick-up element such as a CCD has a photoelectric converting portion and a memory portion as a buffer memory for temporarily accumulating therein image information formed in the converting portion.
In a frame transfer type CCD, for example, the photoelectric converting portion is used as a transfer path for transferring the charge in the photoelectric converting portion to the memory portion and therefore, a time equal to the number of picture elements in the vertical direction of the photoelectric converting portion divided by the CCD driving frequency is required for the transfer period. That is, assuming that the number of vertical picture elements is 500 and the driving frequency is 10 MHz, a time of 50 .mu.sec. is necessary.
Where the image of an ordinary object is to be picked up, the quantity of light entering the photoelectric converting portion as the transfer path during this transfer period is negligibly small. However, where image pick-up is effected by the use of an auxiliary illuminating light source, very intense light may enter within a short time.
For example, assuming a flashlight source like a popular strobe light source as the illuminating light source, a time of about 20 .mu.sec. is required until a peak is reached after triggering and thereafter a trail of about 1.8 msec. is left, as shown in FIG. 1 of the accompanying drawings.
Accordingly, if the light source emits light when one-half of the picture element signal in the vertical direction, as shown in FIG. 2 of the accompanying drawings, has been transferred from the photoelectric converting portion 1 to the memory portion 2, the upper half 3 of the picture plane under transfer will become light and the lower half 4 will become dark.
Such a phenomenon is more liable to occur not only in the case of the strobe light source as described above but also in the case of any auxiliary light source as the quantity of emitted light is greater and the period of light emission is longer.
On the other hand, in the case of the conventional image pick-up elements such as the CCD, no shutter is provided forwardly of the light-receiving surface thereof and therefore, there is no limitation on the exposure time associated with the opening-closing speed of the shutter.
It is possible also to reduce the image accumulating time in the photoelectric converting portion to, for example, the order of one several hundredsth of a second, i.e., the order of one to several msec., and this is a feature of the image pick-up device using such image pick-up elements.
However, the shorter the accumulating time is made in this manner, the more liable to occur is brightness irregularity of the picture plane due to the auxiliary light source as shown in FIG. 2.
Also, where the object to be photographed is very dark, it is impossible to render the exposure amount optimum solely by control of the accumulating time and the diaphragm. Thus, an auxiliary illuminating light source becomes necessary and in that case, heretofore, the brightness of the object has been detected by a sensor such as an SPC (silicon photo cell) and adjustment or the like of the illuminating device has been effected on the basis of the output of such sensor, but this would complicate the construction for detecting the brightness of the object.